1. Field of the Invention
The present invention relates to a drive shaft supporting structure for a small boat, in which the drive shaft supporting structure rotatably supports a drive shaft which transmits engine output to a water jet pump.
2. Description of the Background Art
Small personal watercraft, which include a boat body composed of a hull and a deck, are well known. In this type of boat, the hull, which constitutes a lower portion of the boat body, is covered with the deck, which constitutes an upper portion of the boat body. An engine is provided in the boat body, and a water jet pump is mounted to a rear portion of the boat body. Water is drawn into the water jet pump via a water introduction channel formed in the bottom of the hull. The water jet pump is driven by the engine, via a drive shaft, and the drawn water is jetted rearwardly in order to propel the boat forward.
The small boat is propelled due to the action of the water jet pump, and is provided with a recess directed downwardly on a rear bottom portion of the hull. The water jet pump is stored in a rear part of the recess, and a part of the recess disposed in front of the pump is configured to be the water introduction channel where water is drawn into the pump.
The drive shaft extends from the engine toward the rear of the boat body, and connects the engine to the water jet pump. In order to connect the engine disposed in the boat body with the water jet pump, disposed in the recess, the drive shaft passes through an opening provided in a wall of the water introduction channel. The drive shaft is rotatably supported within the opening by a drive shaft supporting structure provided on the boat body.
In order to extend the drive shaft from inside the boat body toward the outside thereof, it is necessary to form the opening in the wall of the water introduction channel. Therefore, the drive shaft supporting structure is configured to prevent water from entering the boat body through the opening. Such a configuration is disclosed, for example, in Japanese published patent document JP-A-2004-58871.
The drive shaft supporting structure disclosed in JP-A-2004-58871 is configured in such a manner that an inclined wall, that defines the water introduction channel of the hull, is formed with a recess directed toward the front of the hull. A rubber joint member is inserted into the recess, and a cylindrical portion of the joint member projects from the opening of the recess toward the front of the hull.
A rubber cylindrical fitting member fits on the outside of the cylindrical portion which projects from the opening, and the cylindrical fitting member is tightened onto the cylindrical portion with a tightenable band clamp. For example, a hose clamp can be used to adjustably secure the cylindrical fitting member to the cylindrical portion. Accordingly, the cylindrical fitting member tightly adheres to the cylindrical portion by the tightenable band clamp.
The cylindrical fitting member is integrally formed with a shaft-supporting member, and a flange of the shaft-supporting member is secured to a cover with a bolt. The cover is fixed to the hull. The shaft-supporting member is a bearing that rotatably supports the drive shaft, and a clearance between the bearing and the drive shaft is hermetically sealed with a sealing material. Consequently, the sealing material prevents water that has entered from the interior of the water introduction channel into the cylindrical fitting member from entering into the hull.
Now, a main reason why the recess is formed on the inclined wall of the water introduction channel will be described.
The water introduction channel is a channel for introducing water to the pump, and in order to permit smooth flow of water in the water introduction channel, it is necessary to prevent the joint member from projecting toward the water introduction channel. Therefore, as described above, the recess is formed on the inclined wall of the water introduction channel so as to be directed toward the front of the hull, and the rubber joint member is inserted into the recess. Accordingly, the joint member can be prevented from projecting toward the water introduction channel.
As described above, the hull disclosed in JP-A-2004-58871 is formed with the recess directed toward the front of the hull, and is provided with a cover. Therefore, the shape of the hull is relatively complex, which increases the cost of the hull.
When assembling the drive shaft supporting structure to the hull, the rubber joint member is inserted into the recess of the hull, and the cylindrical portion projects from the opening. Subsequently, the cylindrical fitting member is fitted on the cylindrical portion, and the shaft-supporting member is secured to the cover with a bolt. Then, the tightenable band is tightened to bring the cylindrical fitting member into tight adhesion with the cylindrical portion, whereby assembly of the drive shaft supporting structure to the hull is completed.
The hull is a relatively large member, and hence it is difficult to frequently change the orientation of the hull. Therefore, during the process of assembling the drive shaft supporting structure to the hull, the hull is normally kept in a horizontal orientation with the hull bottom directed downward.
Therefore, when inserting the rubber joint member into the recess of the hull or causing the cylindrical portion to be projected from the opening, the assembler is required to proceed with the assembly operation in a relatively uncomfortable posture in order to align his/her body with the recess of the hull. In the same manner, when fitting the cylindrical fitting member to the cylindrical portion, or bringing the cylindrical fitting member into tight adhesion with the cylindrical portion by tightening the tightenable band clamp, the assembler is required to proceed with the assembly operation in a relatively uncomfortable posture in order to align his/her body with the cylindrical portion.
In this manner, the assembler is required to proceed with the assembling work of the drive shaft supporting structure while maintaining the relatively uncomfortable posture so as to align his/her body with the hull, and as a consequence, manufacturing productivity is impaired.